class_docstr: Construct a BertGeneration tokenizer. Based on [SentencePiece](https://github.com/google/sentencepiece).
  
  This tokenizer inherits from [`PreTrainedTokenizer`] which contains most of the main methods. Users should refer to
  this superclass for more information regarding those methods.
  
  Args:
      vocab_file (`str`):
          [SentencePiece](https://github.com/google/sentencepiece) file (generally has a *.spm* extension) that
          contains the vocabulary necessary to instantiate a tokenizer.
      bos_token (`str`, *optional*, defaults to `"<s>"`):
          The begin of sequence token.
      eos_token (`str`, *optional*, defaults to `"</s>"`):
          The end of sequence token.
      unk_token (`str`, *optional*, defaults to `"<unk>"`):
          The unknown token. A token that is not in the vocabulary cannot be converted to an ID and is set to be this
          token instead.
      pad_token (`str`, *optional*, defaults to `"<pad>"`):
          The token used for padding, for example when batching sequences of different lengths.
      sep_token (`str`, *optional*, defaults to `"<::::>"`):
          The separator token, which is used when building a sequence from multiple sequences, e.g. two sequences for
          sequence classification or for a text and a question for question answering. It is also used as the last
          token of a sequence built with special tokens.
      sp_model_kwargs (`dict`, *optional*):
          Will be passed to the `SentencePieceProcessor.__init__()` method. The [Python wrapper for
          SentencePiece](https://github.com/google/sentencepiece/tree/master/python) can be used, among other things,
          to set:
  
          - `enable_sampling`: Enable subword regularization.
          - `nbest_size`: Sampling parameters for unigram. Invalid for BPE-Dropout.
  
            - `nbest_size = {0,1}`: No sampling is performed.
            - `nbest_size > 1`: samples from the nbest_size results.
            - `nbest_size < 0`: assuming that nbest_size is infinite and samples from the all hypothesis (lattice)
              using forward-filtering-and-backward-sampling algorithm.
  
          - `alpha`: Smoothing parameter for unigram sampling, and dropout probability of merge operations for
            BPE-dropout.
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docstr: Converts a sequence of tokens (string) in a single string.
docstr_tok: ["Converts","a","sequence","of","tokens","(","string",")","in","a","single","string","."]
code: def convert_tokens_to_string(self, tokens):
      """Converts a sequence of tokens (string) in a single string."""
      current_sub_tokens = []
      out_string = ""
      for token in tokens:
          # make sure that special tokens are not decoded using sentencepiece model
          if token in self.all_special_tokens:
              out_string += (
                  self.sp_model.decode(current_sub_tokens) + token
              )
              current_sub_tokens = []
          else:
              current_sub_tokens.append(token)
      out_string += self.sp_model.decode(current_sub_tokens)
      return out_string.strip()
  
file_path: transformers/src/transformers/models/bert_generation/tokenization_bert_generation.py
imports: import os
  from shutil import copyfile
  from typing import Any, Dict, List, Optional, Tuple
  import sentencepiece
  from ...tokenization_utils import PreTrainedTokenizer
  from ...utils import logging
label_desc: Use image node_id 9 for calling the BertGenerationTokenizer obj's underlying member method code with example usage: obj.convert_tokens_to_string(tokens) and returns: out_string